Precessional spin current structure with non-magnetic insertion layer for MRAM

ABSTRACT

A magnetoresistive random-access memory (MRAM) is disclosed. MRAM device has a magnetic tunnel junction stack having a significantly improved performance of the free layer in the magnetic tunnel junction structure. The MRAM device utilizes a precessional spin current (PSC) magnetic structure in conjunction with a perpendicular MTJ where the in-plane magnetization direction of the PSC magnetic layer is free to rotate. The precessional spin current magnetic layer a first and second precessional spin current ferromagnetic layer separated by a nonmagnetic precessional spin current insertion layer.

FIELD

The present patent document relates generally to spin-transfer torquemagnetic random access memory and, more particularly, to a magnetictunnel junction stack having improved performance of the free layer inthe magnetic tunnel junction structure through use of a precessionalspin current structure having in plane anisotropy through use offerromagnetic materials and a nonmagnetic spacer layer.

BACKGROUND

Magnetoresistive random-access memory (“MRAM”) is a non-volatile memorytechnology that stores data through magnetic storage elements. Theseelements are two ferromagnetic plates or electrodes that can hold amagnetization and are separated by a nonmagnetic material, such as anonmagnetic metal or insulator. In general, one of the plates has itsmagnetization pinned (i.e., a “reference layer”), meaning that thislayer has a higher coercivity than the other layer and requires a largermagnetic field or spin-polarized current to change the orientation ofits magnetization. The second plate is typically referred to as the freelayer and its magnetization direction can be changed by a smallermagnetic field or spin-polarized current relative to the referencelayer. The insulator between the reference layer and the free layerenables tunneling of electrons from the free layer to the referencelayer.

MRAM devices store information by changing the orientation of themagnetization of the free layer. In particular, based on whether thefree layer is in a parallel or anti-parallel alignment relative to thereference layer, either a “1” or a “0” can be stored in each MRAM cell.Due to the spin-polarized electron tunneling effect, the electricalresistance of the cell change due to the orientation of themagnetization of the two layers. The cell's resistance will be differentfor the parallel and anti-parallel states and thus the cell's resistancecan be used to distinguish between a “1” and a “0”. One importantfeature of MRAM devices is that they are non-volatile memory devices,since they maintain the information even when the power is off. The twoplates can be sub-micron in lateral size and the magnetization directioncan still be stable with respect to thermal fluctuations.

Spin transfer torque or spin transfer switching, uses spin-aligned(“polarized”) electrons to change the magnetization orientation of thefree layer in the magnetic tunnel junction. In general, electronspossess a spin, a quantized number of angular momentum intrinsic to theelectron. An electrical current is generally unpolarized, i.e., itconsists of 50% spin up and 50% spin down electrons. Passing a currentthough a magnetic layer polarizes electrons with the spin orientationcorresponding to the magnetization direction of the magnetic layer(i.e., polarizer), thus produces a spin-polarized current. If aspin-polarized current is passed to the magnetic region of a free layerin the magnetic tunnel junction device, the electrons will transfer aportion of their spin-angular momentum to the magnetization layer toproduce a torque on the magnetization of the free layer. Thus, this spintransfer torque can switch the magnetization of the free layer, which,in effect, writes either a “1” or a “0” based on whether the free layeris in the parallel or anti-parallel states relative to the referencelayer.

FIG. 1 illustrates a magnetic tunnel junction (“MTJ”) stack 100 for aconventional MRAM device. As shown, stack 100 includes one or more seedlayers 110 provided at the bottom of stack 100 to initiate a desiredcrystalline growth in the above-deposited layers. Furthermore, MTJ 130is deposited on top of SAF layer 120. MTJ 130 includes reference layer132, which is a magnetic layer, a nonmagnetic tunneling barrier layer(i.e., the insulator) 134, and the free layer 136, which is also amagnetic layer. It should be understood that reference layer 132 isactually part of SAF layer 120, but forms one of the ferromagneticplates of MTJ 130 when the nonmagnetic tunneling barrier layer 134 andfree layer 136 are formed on reference layer 132. As shown in FIG. 1,magnetic reference layer 132 has a magnetization direction perpendicularto its plane. As also seen in FIG. 1, free layer 136 also has amagnetization direction perpendicular to its plane, but its directioncan vary by 180 degrees.

The first magnetic layer 114 in the SAF layer 120 is disposed over seedlayer 110. SAF layer 120 also has a antiferromagnetic coupling layer 116disposed over the first magnetic layer 114. Furthermore, a nonmagneticspacer 140 is disposed on top of MTJ 130 and a polarizer 150 is disposedon top of the nonmagnetic spacer 140. Polarizer 150 is a magnetic layerthat has a magnetic direction in its plane, but is perpendicular to themagnetic direction of the reference layer 132 and free layer 136.Polarizer 150 is provided to polarize a current of electrons(“spin-aligned electrons”) applied to MTJ structure 100. Further, one ormore capping layers 160 can be provided on top of polarizer 150 toprotect the layers below on MTJ stack 100. Finally, a hard mask 170 isdeposited over capping layers 160 and is provided to pattern theunderlying layers of the MTJ structure 100, using a reactive ion etch(RIE) process.

Various mechanisms have been proposed to assist the free-layermagnetization switching in magnetic tunnel junction (MTJ) devices suchas orthogonal spin transfer for in-plane magnetic tunnel junctions. Oneissue has been that to realize the orthogonal spin transfer effect forin-plane MTJ structures, large spin currents may be required forswitching. The need for large switching currents may limit such device'scommercial applicability. One way proposed to reduce switching currentis to lower the magnetization of the free layer. However, if theeffective magnetization of the free layer is lowered significantly, theorthogonal effect has to be limited so that the free-layer does not gointo precessional mode that would make the end state of the free-layermagnetization un-deterministic. This defines the operation window forthe in-plane OST structures. In an in-plane device, unlike that shown inFIG. 1, the magnetization direction of the reference layer and freelayer are in the plane of the layer. Another aspect of in-plane devicesis that the thermal stability requirements may limit the size of the MTJdevices to approximately sixty nanometers or higher.

For perpendicular MTJ structures such as those shown in FIG. 1, theprecession is not an issue. The orthogonal polarizer acts on the freelayer magnetization at the initial state, but when the precession takeshold, the fixed orthogonal polarizer 150 helps only half the cycle ofthe free-layer magnetization rotation while it harms the other half ofthe cycle. This is demonstrated with reference to FIGS. 2A-2B and 3.FIGS. 2A-2B shows switching of a free layer 136 of an MTJ. As is seen,free layer 136 has a magnetization direction 200 perpendicular to thatof the polarizer 150. The magnetization direction 200 of the free layer136 can rotate by 180 degrees. FIGS. 2A-2B show precession about theaxis of the magnetization vector of free layer 136. During precession,magnetic vector 200 begins to rotate about its axis in a cone-likemanner such that its magnetization vector 200′ deflects from theperpendicular axis 202 of free layer 136. For an ideal case, prior toinitiating precession, no component of magnetic vector 200 is in theplane of free layer 136, once precession starts, a component of magneticvector 200′ can be found both in-plane and orthogonal to free layer 136.As magnetic vector 200′ continues to precess (i.e., switch), therotation of vector 200′ extends further from the center of free layer136, as is seen in FIG. 2B.

In prior MTJ devices using a polarizer such as polarizer 150, themagnetization direction of polarizer 150 is fixed, which is shown inFIGS. 1 and 3. See also U.S. Pat. No. 6,532,164, which states that thedirection of the magnetization of the polarizing layer cannot vary inthe presence of current. Prior to current passing through the MTJ, thefree layer 136 has a magnetization direction 200 substantiallyperpendicular to that of the polarizer 150. While the magnetizationdirection 200 of the free layer 136 can rotate by 180 degrees, suchrotation is normally precluded by the free layer's inherent dampingability 205, which is represented by a vector 205 pointing to axis 202(shown as a dashed line in FIG. 2A as well as FIG. 3). Axis 202 isperpendicular to the plane of free layer 136. This damping 205 hasvalue, defined by the damping constant, which maintains themagnetization direction of the free layer 136.

Passing a current through polarizer 150 produces a spin-polarizedcurrent, which creates a spin transfer torque 210 in the direction ofthe polarizer 150 on the magnetization vector 200. This spin transfertorque from the polarizer adds to the main spin transfer torque thatcauses free layer magnetization direction switching. In devices likethose shown in FIG. 1, when the spin transfer torque 210 begins to helpovercome the damping 205 inherent to the free layer 136, the magneticdirection 200′ begins to precess about its axis, as shown in FIG. 2A. Asseen in FIG. 3, spin transfer torque 210 helps the magnetizationdirection of the free layer 136 to precess in a cone-like manner aroundan axis 202 perpendicular to the plane of the layers. When a spinpolarized current traverses the stack 100, the magnetization of the freelayer 136 precesses in a continuous manner (i.e. it turns on itself in acontinuous manner as shown in FIG. 3) with maintained oscillations untilthe magnetic direction of free layer 136 is opposite the magneticdirection prior to the spin torque causing precession, i.e., themagnetic direction of free layer 136 switches by 180 degrees.

FIG. 3 illustrates precession of a free layer 136 of an MTJ assisted byspin polarized current provided by polarizing magnetic layer 150. Thespin polarized electrons from polarizer 150 provide torque 210 thathelps overcome the damping 205 in the first half of the precession 215because the torque 210 provided by the spin polarized current isopposite that of the inherent damping 205 of the free layer 136. This isshown on the right-hand side of the middle portion of FIG. 3. However,the spin polarized electrons from polarizer 150 actually harm theswitching process during the second half of the precession 220. Thereason for this is that the spin of the electrons in the spin polarizedcurrent only apply a torque 210 in the direction of their polarization.Thus, when the magnetic vector is in the half of the precession cycle220 that is opposite the spin of the polarized electrons, the spintransfer torque 210 actually works with the inherent damping 205 of freelayer 136 to make rotation more difficult. This is shown in theleft-hand side of the middle portion of FIG. 3. Indeed, it is themagnetization vector of the reference layer 132 (not shown in FIG. 3)that overcomes the damping of free layer 136 as well as the spintransfer torque 210 during the half of a precession cycle where the spinof the electrons harms precession, and thus it is the reference layer132 that allows for completion of precession.

In these prior devices, because magnetization direction of polarizer 150is fixed, once the precession holds, it has no positive effect on theswitching mechanism for a full one-hundred eighty degree precession.This is because polarized electrons will help the spin transfer torquethe most when all vectors are closely aligned.

U.S. patent application Ser. No. 14/814,036, filed by the same Applicantas the present patent document, discloses an MRAM device having aprecessional spin current (“PSC”) magnetic layer that is physicallyseparated from the free magnetic layer of a magnetic tunnel junction andwhich is coupled to the free magnetic layer by a nonmagnetic spacer. Inthe device described in this co-pending application, the magnetizationdirection of the precessional spin current magnetic layer followsprecession of the magnetization direction of the free magnetic layer,thereby causing spin transfer torque to assist switching of themagnetization vector of the free magnetic layer. The disclosure of U.S.patent application Ser. No. 14/814,036 is incorporated by reference inits entirety.

The performance of an MRAM device using a single ferromagnetic layer forthe precessional spin current magnetic layer varies based on itsthickness and the choice of materials. The ability to vary the thicknessof the precessional spin current magnetic layer is important becausethickness can affect the influence of the precessional spin currenteffect on switching of the free layer of the magnetic tunnel junction.The same is true for material selection. Indeed, thickness and materialselection impact spin torque efficiency of the PSC structure as well asthe coupling strength between the PSC structure and the free layer.

The magnetic moment of in-plane ferromagnetic precessional spin currentmagnetic layer has to be significant in order to develop sufficient spinpolarization of current passing there through. The required exchangecoupling between the precessional spin current magnetic layer and thefree layer of the magnetic tunnel junction needed to achieve aprecession of the precessional spin current magnetic layer with the freelayer may also require a narrow window of exchange coupling strength.Additionally a dipolar field produced by the close proximity of in-planePSC layer to the free layer can cause a decrease in the stability of thefree layer due to strong magneto-static coupling. The variousembodiments described herein overcome these issues.

SUMMARY

An precessional spin current structure for an MRAM device having amagnetic tunnel junction stack is disclosed.

In an embodiment, a magnetic device includes a first syntheticantiferromagnetic structure in a first plane. The first syntheticantiferromagnetic structure includes a magnetic reference layer. Themagnetic reference layer has a magnetization vector that isperpendicular to the first plane and has a fixed magnetizationdirection. An embodiment also includes a nonmagnetic tunnel barrierlayer in a second plane and disposed over the magnetic reference layer.An embodiment includes a free magnetic layer in a third plane anddisposed over the nonmagnetic tunnel barrier layer. The free magneticlayer has a magnetization vector that is perpendicular to the thirdplane and has a magnetization direction that can precess from a firstmagnetization direction to a second magnetization direction. Themagnetic reference layer, the nonmagnetic tunnel barrier layer and thefree magnetic layer form a magnetic tunnel junction. An embodiment alsoincludes a nonmagnetic spacer layer in a fourth plane and disposed overthe free magnetic layer. The magnetic coupling layer comprises MgO. Anembodiment also includes a precessional spin current magnetic structurein a fifth plane that is physically separated from the free magneticlayer and coupled to the free magnetic layer by the nonmagnetic spacerlayer. The precessional spin current magnetic structure has amagnetization vector with a magnetization direction in the fifth planewhich can freely rotate in any magnetic direction in the fifth plane.The precessional spin current magnetic structure comprises a firstprecessional spin current ferromagnetic layer, a nonmagneticprecessional spin current insertion layer and a second precessional spincurrent ferromagnetic layer. The first precessional spin currentferromagnetic layer can be disposed over the nonmagnetic spacer layer.The nonmagnetic precessional spin current insertion layer can bedisposed over the first precessional spin current ferromagnetic layer.The second precessional spin current ferromagnetic layer can be disposedover the nonmagnetic precessional spin current insertion layer. In anembodiment, the magnetic devices further includes a capping layer in asixth plane and disposed over the precessional spin current magneticstructure. In an embodiment, electrons of an electrical current passingthrough the precessional spin current magnetic structure are aligned inthe magnetic direction of the precessional spin current magnetic layerand injected into the nonmagnetic spacer, the free magnetic layer, thenonmagnetic tunnel barrier layer, and the magnetic reference layer, andwherein the magnetization direction of the precessional spin currentmagnetic structure precesses, thereby causing spin transfer torque toassist switching of the magnetization vector of the free magnetic layer.

In an embodiment of the magnetic device, the nonmagnetic precessionalspin current insertion layer is constructed of a material having a spindiffusion length exceeding two (2) nanometers.

In an embodiment of the magnetic device, the nonmagnetic precessionalspin current insertion layer is constructed of a thin film of Ru.

In an embodiment of the magnetic device, the thin film of Ru has athickness of at least one nanometer.

In an embodiment of the magnetic device, the thin film of Ru has athickness of 1.5 nanometers.

In an embodiment of the magnetic device, the first precessional spincurrent ferromagnetic layer comprises a thin film of Fe. The nonmagneticprecessional spin current insertion layer comprises a material with along spin diffusion length. The second precessional spin currentferromagnetic layer comprises a thin film of CoFeB.

In an embodiment of the magnetic device, the thin film of Fe has athickness of 0.4 nanometers.

In an embodiment of the magnetic device, the thin film of Fe has athickness of 0.6 nanometers.

In an embodiment of the magnetic device, the thin film of CoFeB iscomprised of forty percent Co, forty percent Fe and twenty percent B.

In an embodiment of the magnetic device, the thin film of CoFeB has athickness of 1.7 nanometers.

In an embodiment of the magnetic device, the thin film of CoFeB has athickness of 1.85 nanometers.

In an embodiment of the magnetic device, the material with a long spindiffusion length is selected from the group consisting of Ru, Cu, Ag,Au, Mg and Al.

In an embodiment of the magnetic device, the free magnetic layer has aneffective magnetic anisotropy such that its easy axis magnetization axispoints away from the perpendicular direction and forms an angle withrespect to perpendicular plane.

An embodiment, a method manufacturing a magnetic device is disclosed,which comprises depositing a first synthetic antiferromagnetic structureover a substrate. The first synthetic antiferromagnetic structure is ina first plane and has a magnetization vector that is perpendicular tothe first plane and has a fixed magnetization direction. The methodincludes depositing an exchange coupling layer over the first syntheticantiferromagnetic structure, where the exchange coupling layer being ina second plane. The method also includes depositing a second syntheticantiferromagnetic structure over the substrate. The second syntheticantiferromagnetic structure is in a third plane. The second syntheticantiferromagnetic structure includes a magnetic reference layer. Thesecond synthetic antiferromagnetic structure and the magnetic referencelayer having a magnetization vector that is perpendicular to the thirdplane and has a fixed magnetization direction. The method also includesdepositing a nonmagnetic tunnel barrier layer in a fourth plane. Thenonmagnetic tunnel barrier is disposed over the magnetic referencelayer. The method also includes depositing a free magnetic layer in afifth plane. The free magnetic layer is disposed over the nonmagnetictunnel barrier layer and has a magnetization vector that isperpendicular to the fifth plane. The free magnetic layer has amagnetization direction that can precess from a first magnetizationdirection to a second magnetization direction. The magnetic referencelayer, the nonmagnetic tunnel barrier layer and the free magnetic layerform a magnetic tunnel junction. The method also includes depositing anonmagnetic spacer layer in a sixth plane that is disposed over the freemagnetic layer. The method further includes depositing a precessionalspin current magnetic structure in a seventh plane that is physicallyseparated from the free magnetic layer and coupled to the free magneticlayer by the nonmagnetic spacer layer. The precessional spin currentmagnetic structure has a magnetization vector with a magnetizationdirection in the seventh plane which can freely rotate in any magneticdirection in the seventh plane.

A method of depositing the precessional spin current magnetic structureincludes depositing a first precessional spin current ferromagneticlayer. The first precessional spin current ferromagnetic layer isdisposed over the nonmagnetic spacer layer. The method of furtherincludes depositing a nonmagnetic precessional spin current insertionlayer. The nonmagnetic precessional spin current insertion layer isdisposed over the first precessional spin current ferromagnetic layer.The method further includes depositing a second precessional spincurrent ferromagnetic layer. The second precessional spin currentferromagnetic layer is disposed over the nonmagnetic precessional spincurrent insertion layer.

The method of manufacturing the magnetic device further includesdepositing a capping layer in an eighth plane. The capping layer beingdisposed over the precessional spin current magnetic layer. The methodfurther includes annealing the magnetic device at a temperature of 400degrees Celsius or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included as part of the presentspecification, illustrate the presently preferred embodiments and,together with the general description given above and the detaileddescription given below, serve to explain and teach the principles ofthe MTJ devices described herein.

FIG. 1 illustrates a conventional MTJ stack for an MRAM device.

FIGS. 2A-2B illustrate the precession of the free layer in an MTJ.

FIG. 3 illustrates the precession of the free layer in an MTJ used witha polarizing magnetic layer having a fixed magnetization direction.

FIG. 4 illustrates the precession of the free layer in an MTJ used witha precessional spin current magnetic layer having a magnetizationdirection that rotates freely.

FIG. 5 illustrates an MTJ stack for an embodiment of an MRAM devicehaving a precessional spin current magnetic layer.

FIGS. 6A-6B is a flow chart showing manufacturing steps for anembodiment of an MRAM device having a precessional spin current magneticlayer as described herein.

FIG. 7 illustrates an embodiment of an MTJ stack for an MRAM devicehaving a precessional spin current magnetic layer with a nonmagneticprecessional spin current insertion layer.

FIGS. 8A-8B is a flow chart showing manufacturing steps for anembodiment of an MRAM device having a precessional spin current magneticlayer as described herein.

FIG. 9 illustrates another embodiment of an MTJ stack for an MRAM devicehaving a precessional spin current magnetic layer with a nonmagneticprecessional spin current insertion layer.

FIG. 10 illustrates the magnetic direction of the precessional spincurrent magnetic layer of an embodiment.

FIG. 11 is a graph of the thin film vibrating sample magnetometer (VSM)major hysteresis loop data for the device illustrated in FIG. 7 wherethe magnetic field is applied perpendicular to the plane of the devicelayers.

FIG. 12 is a graph of the thin film vibrating sample magnetometer (VSM)major hysteresis loop data for the device illustrated in FIG. 7 wherethe magnetic field is applied in the plane of the device layers.

FIG. 13 is a graph illustrating ferromagnetic resonance (FMR) of an MRAMdevice illustrated in FIG. 7 having a precessional spin current magneticlayer.

FIG. 14 is an alternative embodiment of an MTJ stack for an MRAM devicehaving a precessional spin current magnetic layer with a nonmagneticprecessional spin current insertion layer.

The figures are not necessarily drawn to scale and the elements ofsimilar structures or functions are generally represented by likereference numerals for illustrative purposes throughout the figures. Thefigures are only intended to facilitate the description of the variousembodiments described herein; the figures do not describe every aspectof the teachings disclosed herein and do not limit the scope of theclaims.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to create and use a precessional spin current structure for amagnetic semiconductor device such as an MRAM device. Each of thefeatures and teachings disclosed herein can be utilized separately or inconjunction with other features to implement the disclosed system andmethod. Representative examples utilizing many of these additionalfeatures and teachings, both separately and in combination, aredescribed in further detail with reference to the attached drawings.This detailed description is merely intended to teach a person of skillin the art further details for practicing preferred aspects of thepresent teachings and is not intended to limit the scope of the claims.Therefore, combinations of features disclosed in the following detaileddescription may not be necessary to practice the teachings in thebroadest sense, and are instead taught merely to describe particularlyrepresentative examples of the present teachings.

In the following description, for purposes of explanation only, specificnomenclature is set forth to provide a thorough understanding of thepresent teachings. However, it will be apparent to one skilled in theart that these specific details are not required to practice the presentteachings.

This present patent document discloses a MRAM device that does not use apolarization layer having a fixed magnetization direction. Instead of apolarization layer having a fixed magnetization direction, the MRAMdevice described in this patent document utilizes a precessional spincurrent (PSC) magnetic layer 350 in conjunction with a perpendicular MTJ430 where the in-plane magnetization component direction of the PSClayer is free to rotate (and is shown, for example, in FIG. 4). PSCmagnetic layer 350 can rotate with the free-layer magnetizationprecessional dynamics. This will significantly improve the impact of thespin current in overcoming the inherent damping 205 of the free layer336 since the PSC layer will help the spin torque overcome this dampingthrough the entire orbital motion of the precession cycle rather on onlyhalf of the precession. This precessional spin current effect throughoutthe entire one-hundred eighty degree rotation significantly enhances thefree-layer magnetization switching.

FIG. 4 shows the concept behind the MRAM device using a PSC magneticlayer 350 having magnetization vector 270 that rotates instead of apolarization layer 150 having a magnetic vector with a fixedmagnetization direction. The free layer 336 in this embodiment issimilar to the free layer 136 previously discussed, in that it has aninherent damping characteristic 205 that can be overcome with theassistance of spin transfer torque. However, the embodiment shown inFIG. 4 replaces polarizing layer 150 with PSC magnetic layer 350. Asseen in the bottom portion of FIG. 4, the direction of the spin transfertorque 310 created by spin current passing through free layer 336changes with the rotation of the magnetization direction of PSC magneticlayer 350. As seen in the middle of FIG. 4, spin transfer torque 310helps the magnetization direction 200′ of the free layer 336 to precessin a cone-like manner around an axis 202 perpendicular to the plane ofthe layers. FIG. 4 shows a progression of rotation of the magneticdirection 200′ about axis 202. As discussed, when a spin polarizedcurrent traverses the device, the magnetization of the free layer 336precesses in a continuous manner (i.e. it turns on itself in acontinuous manner as shown in FIG. 4) with maintained oscillations untilthe magnetic direction of free layer 336 is opposite the magneticdirection prior to the spin torque causing precession, i.e., themagnetic direction of free layer 136 switches by 180 degrees. Theprecessional spin current layer 350 and the free-layer 336 aremagnetically and/or electronically coupled such that the magnetizationdirection of the magnetization vector 270 of the PSC magnetic layer 350is free to follow the precessional rotation of the magnetic vector ofthe free layer 336. This can be seen in FIG. 4.

As seen in on the right-hand side of FIG. 4, the spin polarizedelectrons provide torque 310 helps to overcome the damping 205 in thefirst half of the precession 215 because the torque 310 provided by thespin polarized current is opposite that of the inherent damping 205 ofthe free layer 336. As discussed, the magnetization direction ofmagnetization vector 270 of PSC magnetic layer 350 rotates. Thus, thepolarization of electrons of the spin current created by PSC magneticlayer 350 changes as well. This means that the direction of torque 310exerted on magnetic vector of free layer 336 changes as well, which isseen on the bottom of FIG. 4. Thus, unlike prior devices having a fixedpolarization magnetic layer 150, the spin of the electrons in the spinpolarized current applies a torque 310 in both halves of the precessioncycle, including the half of the precession cycle 220 where devices withfixed polarization magnetic layers 150 actually harmed precession. Thisis seen in the left-hand side of FIG. 4. As is seen, the torque 310continues to help overcome the inherent damping 205 of free layer 136throughout the entire precession cycle.

In an embodiment, the precessional vector 270 of the PSC magnetic layer350 is free to follow the precessional rotation of the magnetic vectorof the free layer 336. The magnetization direction of the free layer isswitched by the spin torque 310 from the reference layer 132 where thedirection of the current defines the final state.

A memory cell with a precessional spin current MTJ structure 300 isshown in FIG. 5. The embodiment shown in FIG. 5, as well as allembodiments described herein, is preferably formed on a siliconsubstrate or other appropriate base for a magnetic device, and caninclude complementary metal oxide semiconductor (CMOS) circuitryfabricated thereon. MTJ structure 300 includes one or more seed layers320 provided at the bottom of stack 300 to initiate a desiredcrystalline growth in the above-deposited layers. A first syntheticantiferromagnetic (SAF) layer 322 is disposed over seed layer 320. Asseen in FIG. 5, first SAF layer 322 is a magnetic layer having amagnetization direction that is perpendicular to its plane. Details ofthe construction of first SAF layer 322 will be discussed below. Ananti-ferromagnetic (AFM) coupling layer 324 is disposed over first SAFlayer 322. AFM coupling layer 324 is a nonmagnetic layer. A second SAFlayer 326 is disposed over AFM coupling layer 324. As seen in FIG. 5,second SAF layer 326 has a magnetic direction that is perpendicular toits plane. In an embodiment, the magnetic direction of first SAF layer322 and second SAF layer 326 are antiparallel, as is shown in FIG. 5.Details of the construction of second SAF layer 326 will also bediscussed below. A ferromagnetic coupling layer 328 is placed oversecond SAF layer 326. Ferromagnetic coupling layer 328 is a nonmagneticlayer. MTJ 330 is deposited over ferromagnetic coupling layer 328. MTJ330 includes reference layer 332, tunneling barrier layer (i.e., theinsulator) 334 and free layer 336. Reference layer 332 of MTJ 330 isfabricated over ferromagnetic coupling layer 328. Tunneling barrierlayer 334 of MTJ 330 is fabricated over reference layer 332. Free layer336 of MTJ 330 is fabricated over tunneling barrier layer 334. Note thatsynthetic antiferromagnetic layer 326 technically also includesferromagnetic coupling layer 328 and reference layer 332, but are shownseparately here for explanation purposes.

As shown in FIG. 5, the magnetization vector of reference layer 332 hasa magnetization direction that is perpendicular to its plane. As alsoseen in FIG. 5, free layer 336 also has a magnetization vector that isperpendicular to its plane, but its direction can vary by 180 degrees.In addition, free layer 336 design may include magnetization of the freelayer 336 pointing a few degrees away from its perpendicular axis. Thetilted angle of the free layer magnetization can be due to interactionwith the PSC magnetic layer 350 or due to magnetocrystalline anisotropy,and will additionally help switching of the free layer magnetization byimproving the initiation of the switching. Because reference layer 332and free layer 336 each have a magnetic direction that is perpendicularto their respective planes, MTJ 330 is known as a perpendicular MTJ.

A nonmagnetic spacer layer 340 is disposed over of MTJ 330. Precessionalspin current (“PSC”) magnetic structure 350 is disposed over nonmagneticspacer layer 340. In one embodiment, PSC magnetic structure 350 has amagnetization vector having a magnetic direction parallel to its plane,and is perpendicular to the magnetic vector of the reference layer 332and free layer 336. One or more capping layers 370 can be provided ontop of PSC layer 350 to protect the layers below on MTJ stack 300.

Nonmagnetic spacer layer 340 has a number of properties. For example,nonmagnetic spacer layer 340 physically separates the free layer 336 andthe PSC structure 350. Nonmagnetic spacer layer 340 transmits spincurrent efficiently from the PSC magnetic structure 350 into the freelayer 336. Nonmagnetic spacer layer 340 also promotes goodmicrostructure and high tunneling magnetoresistance (TMR) and helps keepthe damping constant of the free layer 336 low.

In accordance with the present teachings, PSC magnetic structure 350comprises multiple layers. A first precessional spin current (“PSC”)ferromagnetic layer 343 is formed over nonmagnetic spacer layer 340. Anonmagnetic precessional spin current (“PSC”) insertion layer 345 isformed over first PSC ferromagnetic layer 343. A second precessionalspin current (“PSC”) ferromagnetic layer 347 is formed over nonmagneticPSC insertion layer 345.

The nonmagnetic PSC insertion layer 345 improves performance of PSCmagnetic structure 350 because it allows tailoring of both the staticand dynamic coupling of the PSC magnetic structure 350 to free layer336. The static coupling is exchange coupling while the dynamic couplingis the spin pumping effect.

Separating first and second ferromagnetic PSC layers 343 and 347 bynonmagnetic PSC insertion layer 345 avoids strong magneto-staticcoupling of the PSC magnetic structure 350 to free layer 336. Thisimproves the impact that precession of PSC magnetic structure 350 has onfree layer 336 while also retaining the stability of free layer 336. Inan embodiment, a thin nonmagnetic PSC insertion layer 345 is used, whichcan achieve static and dynamic coupling of first and secondferromagnetic PSC layers 343 and 347 via nonmagnetic PSC insertion layer345. Static coupling takes place via exchange coupling while dynamiccoupling takes place via spin pumping. The static and dynamic couplingcauses precession of the magnetic directions of the magnetic vectors offirst and second ferromagnetic PSC layers 343 and 347. In an embodiment,nonmagnetic PSC insertion layer 345 can have a thickness ranging fromone nanometer to three nanometers. When nonmagnetic PSC insertion layer345 has a thickness of approximately one nanometer, one can achievestatic coupling via exchange and dynamic coupling via spin pumpingeffect of precessing magnetizations of adjacent first and secondferromagnetic PSC layers 343 and 347. When the thickness of nonmagneticPSC insertion layer 345 is greater than one nanometer, the exchangecoupling between adjacent first and second ferromagnetic PSC layers 343and 347 becomes smaller, but dynamic coupling via spin pumping effectwill be present and becomes dominant. This approach provides bettercontrol of the coupling between PSC magnetic structure 350 and freelayer 336.

The spin polarized current that can switch free layer 336 of magnetictunnel junction 330 is provided by PSC magnetic structure 350 by using aspin pumping mechanism and/or exchange coupling which is facilitated vianonmagnetic PSC insertion layer 345. First ferromagnetic PSC layer 343,which can be directly deposited on nonmagnetic spacer layer 340, ensurescontinuity of a spin current generated by the second ferromagnetic PSClayer 347 and transfers the spin polarized electrons of the programmingcurrent to free layer 336. In addition, when a small DC current passesthrough PSC magnetic structure 350, e.g., during a device readoperation, only a small transverse component of the precessing magneticvector of PSC magnetic structure 350 is transferred to free layer 336.This small transverse component of precessing magnetic vector of PSCmagnetic structure 350 is normal to the film plane of PSC magneticstructure 350 and parallel to free layer 336. According to spin pumpingand spin diffusion theory, since the transverse component of precessingmagnetic vector is related to magnetic damping, this contribution canalso be tuned by selecting an appropriate material as well as materialthickness to achieve different magnetic damping coefficient. This inprincipal can contribute to enhanced stabilization of free layer 336 andimprove data retention.

As discussed, an MRAM cell is programmed by passing direct current from,for example, current source 375, through the PSC magnetic structure 350,magnetic tunnel junction 330, and the remaining structures of device300. Current used for programming (e.g., a write operation) can besignificantly higher than current used for read operations. For thehigher DC currents used during a device write operation, theprecessional angle of the magnetic vector of second PSC ferromagneticlayer 347 becomes large. In addition, the in-plane component of themagnetic vector of second PSC ferromagnetic layer 347 is transferred tothe first PSC ferromagnetic layer 343 by spin pumping, which is noworthogonal to free layer 336, thus lowering the energy barrier requiredfor switching of free layer 336. As a result, the amount of switchingcurrent required to switch free layer 336 is reduced when compared toother MRAM devices that use fixed polarizing layers, e.g., polarizerlayer 150 or other PSC magnetic layers.

PSC magnetic structure 350 has the following additional properties.First, in one embodiment, the magnetization direction of PSC magneticstructure 350 is in the plane of the layer but is perpendicular tomagnetization direction of free layer 336. In other embodiments such asshown in FIG. 10, the magnetization direction of PSC magnetic structure350 can have a horizontal component X and perpendicular component Z suchthat the angle Θ between the plane of free layer 336 and the magneticdirection 270 of PSC magnetic structure 350 can be anywhere between 0and less than 90 degrees, although, as discussed, the angle is as closeto zero as feasible so that the magnetic direction remains in-plane.Likewise, as shown, the magnetization vector can also spin in arotational manner, shown in FIG. 10 as cone-like rotation 280 whileprecessing about its perpendicular axis. Note that the angle Θ betweenthe plane of free layer 336 and the magnetic direction 270 of PSCmagnetic layer 350 will vary in this situation.

Seed layer 320 in the MTJ structure shown in FIG. 5 preferably comprisesTa, TaN, Cr, Cu, CuN, Ni, Fe or alloys thereof. First SAF layer 322preferably comprises either a Co/Ni or Co/Pt multilayer structure.Second SAF layer 326 preferably comprises either a Co/Ni or Co/Ptmultilayer structure plus a thin nonmagnetic layer comprised of tantalumhaving a thickness of two to five Angstroms. Anti-ferromagnetic couplinglayer 324 is preferably made from Ru having thickness in the range ofthree to ten Angstroms. Ferromagnetic coupling layer 328 can be made ofa layer of Ta, W, Mo or Hf having a thickness in the range of 1.0 to 10Angstroms. Tunneling barrier layer 334 is preferably made of aninsulating material such as MgO, with a thickness of approximately tenAngstroms. Free layer 336 is preferably made with CoFeB deposited on topof tunneling barrier layer 334. Free layer 336 can also have layers ofFe, Co, Ni or alloys thereof. Spacer layer 340 over MTJ 330 can be anynonmagnetic material such as 2 to 20 Angstroms of Ruthenium, 2-20Angstroms of Ta, 2-20 Angstroms of TaN, 2-20 Angstroms of Cu, 2-20Angstroms of CuN, or 2-20 Angstroms of MgO.

The manner in which a bit is written using the precessional spin currentMTJ structure 300 will now be described. In particular, an electricalcurrent is supplied, for example, by a current source 375, which passeselectrical current through the precessional spin current magneticstructure 350, the nonmagnetic spacer layer 340, the free magnetic layer336, the nonmagnetic tunneling barrier layer 334, and the referencelayer 332. The electrons of the electrical current passing through theprecessional spin current magnetic structure 350 become spin polarizedin the magnetic direction thereof, thus creating a spin polarizedcurrent that passes through nonmagnetic spacer layer 340. The spinpolarized current exerts a spin transfer torque on free magnetic layer336, which helps overcome the inherent damping of the magnetic materialmaking up the free layer 336. This causes the free magnetic layer 336 toprecess about its axis, which is shown in FIG. 4.

Once the magnetic direction of the free magnetic layer 336 begins toprecess, the magnetic direction of the PSC magnetic structure 350 beginsto rotate, as is also seen in FIG. 4. The rotation of the magneticdirection of the PSC magnetic structure 350 causes the spin polarizationof the electrons of the electrical current to change in a mannercorresponding to the magnetic direction of the PSC magnetic structure350. Because the spin of the electrons of the spin polarized currentcorresponds to the magnetic direction of PSC magnetic structure 350, thespin of the electrons applies spin transfer torque to the free layer 336in a direction that varies through an entire switching cycle. Thus,devices using PSC magnetic structure 350 can provide spin transfertorque 310 for an entire switching cycle.

In particular, the structure described herein utilizing PSC magneticstructure 350 and spacer layer 340 creates precessional magnetizationthat provides spin current to the free layer 336 of an MTJ throughoutthe whole precession cycle and therefore significantly enhance the freelayer switching process, which will result in faster write times.

A flowchart showing a method 400 of manufacturing an embodiment of anMRAM stack 500 is illustrated in FIGS. 6A-6B. MRAM stack 500 willnormally be fabricated on some form of substrate, which in certainembodiments can be a silicon substrate. MRAM stack 500 is illustrated inFIG. 7. First step 402 is to deposit seed layer 520. In an embodiment,seed layer 520 can be constructed by depositing, at step 404, a TaNlayer 504 and then, at step 406, depositing a Cu layer 506. In anembodiment, TaN layer 504 is a thin film having a thickness of fivenanometers and Cu layer 506 is a thin film having a thickness of fivenanometers. In alternative embodiments, TaN layer 504 can have athickness ranging from 2 to 20 nanometers while Cu layer 506 can have athickness ranting from 0 to 20 nanometers.

At step 408, first perpendicular synthetic antiferromagnetic layer 522is deposited. In an embodiment, first perpendicular syntheticantiferromagnetic layer 522 can comprise a Pt layer 508 (deposited atstep 410), a Co/Pt multilayer 510 (deposited at step 412) and a Co layer512 (deposited at step 414). In an embodiment, Pt layer 508 is a Pt thinfilm having a thickness of 0.7 nanometers. In other embodiments, Ptlayer 508 can comprise a Pt thin film having a thickness ranging from0.5 to 20 nanometers. Co/Pt multilayer 510 can comprise a thin film ofCo having a thickness of 0.6 nanometers and a thin film of Pt having athickness of 0.4 nanometers. In other embodiments, the Co layer of Co/Ptmultilayer 510 can have a thickness of 0.1 to 1.0 nanometers and the Ptlayer of Co/Pt multilayer 510 can have a thickness ranging from 0.1 to1.0 nanometers. In an embodiment, Co/Pt multilayer 510 is repeated suchthat Co/Pt multilayer 510 comprises six Co/Pt multilayers. In anembodiment, Co layer 512 is a thin film having a thickness of 0.6nanometers. In other embodiments, Co layer 512 can have a thicknessranging from 0.1 to 1.0 nanometers.

As seen in FIG. 7, first perpendicular synthetic antiferromagnetic layer522 has a magnetic vector having a direction perpendicular to its plane.The magnetic direction of first perpendicular syntheticantiferromagnetic layer 522 is fixed and will not change directions(i.e., rotate or precess) under normal operating conditions.

At step 416, exchange coupling layer 524 is deposited. In an embodiment,exchange coupling layer 524 comprises an Ru thin film having a thicknessof 0.8 nanometers, and in other embodiments can range from 0.3 to 1.5nanometers.

At step 418, second perpendicular synthetic antiferromagnetic layer 526is fabricated. Fabrication of second perpendicular syntheticantiferromagnetic layer 526 (step 418) comprises many steps, andincludes fabrication of reference layer 532 of magnetic tunnel junction530, as will be discussed. At step 420, Co layer 514 is deposited. In anembodiment, Co layer 514 is a thin film having a thickness of 0.3nanometers and in other embodiments, can have a thickness of 0.1 to 1.0nanometers. Thereafter, at step 420, a Co/Pt multilayer 516 isdeposited. In an embodiment, Co/Pt multilayer 516 comprises a thin filmof Co having a thickness of 0.6 nanometers and a thin film of Pt havinga thickness of 0.4 nanometers. In other embodiments, the thin film of Cocan have a thickness of 0.1 to 1.0 nanometers while the thin film of Ptcan have a thickness of 0.1 to 1.0 nanometers. Moreover, Co/Ptmultilayer 516 can comprise multiple Co/Pt layers as described herein.In an embodiment, Co/Pt multilayer 516 has two Co/Pt multilayers withthe thickness properties described above. After depositing Co/Ptmultilayer 516 at step 422, the method described herein deposits acobalt layer 518 at step 424. In an embodiment, Co layer 518 is a thinfilm having a thickness of 0.6 nanometers, while other embodiments, Colayer 518 can have a thickness in the range of 0.1 to 1.0 nanometers.Together, Co layer 514, Co/Pt layer 516 and Co layer 518 form a magneticstructure. The magnetic direction of the combination of Co layer 514,Co/Pt layer 516 and Co layer 518 is fixed, perpendicular to the plane ofeach layer, and antiparallel to the magnetic direction of firstperpendicular synthetic antiferromagnetic layer 522.

The magnetic properties of the combination of Co layer 514, Co/Pt layer516 and Co layer 518 will interact with the magnetic properties ofreference layer 532 of second perpendicular synthetic antiferromagneticlayer 526 to generate a magnetic vector having a fixed magneticdirection that is also perpendicular to the plane of each layer ofsecond perpendicular synthetic antiferromagnetic layer 526 andantiparallel to the magnetic direction of first perpendicular syntheticantiferromagnetic layer 522. These magnetic vectors are illustrated andFIG. 7, where it can be seen that the second perpendicular syntheticantiferromagnetic layer 526 has a fixed and perpendicular magneticdirection that is antiparallel to the magnetic direction of firstperpendicular synthetic antiferromagnetic layer 522. Note that themagnetic directions of second perpendicular synthetic antiferromagneticlayer 526 and first perpendicular synthetic antiferromagnetic layer 522are fixed under normal operating conditions.

After deposition of Co layer 518 (step 424), a ferromagnetic couplinglayer 528 is deposited (step 526). In an embodiment, ferromagneticcoupling layer 528 is a thin film of Ta having a thickness of 0.2nanometers. In other embodiments, ferromagnetic coupling layer 528 canbe a thin film of Ta, W, Hf or Mo having a thickness ranging from 0.1 to1.0 nanometers.

After deposition of ferromagnetic coupling layer 528 at step 426,reference layer 532 is deposited (step 428). Step 428, fabrication ofreference layer 532, comprises several steps, including deposition ofmagnetic layer 527 (step 430), deposition of a tungsten (W) layer 529(step 432) and deposition of magnetic layer 531 (step 434). In anembodiment, magnetic layer 527 comprises a thin film of CoFeB comprisedof sixty percent iron (Fe), twenty percent cobalt (Co) and twentypercent boron (B), where the thin film has a thickness of 0.6nanometers. In an embodiment, W layer 529 comprises a thin film having athickness of 0.2 nanometers. In an embodiment, magnetic layer 531comprises a thin film of CoFeB comprised of sixty percent iron (Fe),twenty percent cobalt (Co) and twenty percent boron (B), where the thinfilm has a thickness of 0.8 nanometers. In other embodiments, magneticlayer 527 can comprise a thin film of CoFeB having a thickness rangingfrom 0.5 to 1.5 nanometers, W layer 529 can comprise a thin film havinga thickness of 0.1 to 1.0 nanometers, and magnetic layer 531 cancomprise a thin film of CoFeB having a thickness of 0.5 to 2.0nanometers.

Reference layer 532 is constructed using magnetic materials so that ithas a magnetic vector having a magnetic direction perpendicular to itsplane, is fixed in direction, and is antiparallel to the magneticdirection of first perpendicular synthetic antiferromagnetic layer 522.As discussed and as seen in FIG. 7, the collective materials of thesecond perpendicular synthetic antiferromagnetic layer 526 have amagnetic vector having a magnetic direction that is perpendicular to theplane of each of its collective layers, is fixed in direction andantiparallel to the magnetic direction of first perpendicular syntheticantiferromagnetic layer 522. Note that the particular magnetic directionof first perpendicular synthetic antiferromagnetic layer 522 and secondperpendicular synthetic antiferromagnetic layer 526 is not important, solong as they are perpendicular to their respective planes andantiparallel to each other.

As discussed, reference layer 532 is one of the structures formingmagnetic tunnel junction 530. The flowchart showing the method ofmanufacturing MRAM stack 500, including magnetic tunnel junction 530,continues on FIG. 6B. At step 436, nonmagnetic tunneling barrier layer534 is deposited on reference layer 532. In an embodiment, nonmagnetictunneling barrier 534 is formed as a thin film of an insulatingmaterial, e.g., MgO, and has a thickness of 1.1 nm. The purpose ofnonmagnetic tunneling barrier 534 is discussed above.

Manufacture of magnetic tunnel junction 530 continues at step 438, whenfree layer 536 is deposited over nonmagnetic tunneling barrier 534.Fabrication of free layer 536 comprises several steps. At step 440, amagnetic layer 535 is deposited over nonmagnetic tunneling barrier 534.In an embodiment, magnetic layer 535 is comprised of a thin film ofCoFeB comprised of sixty percent iron (Fe), twenty percent cobalt (Co)and twenty percent boron (B), and having a thickness of 1.2 nanometers.In other embodiments, magnetic layer 535 can comprise a thin film ofCoFeB or other suitable magnetic material having a thickness rangingfrom 0.5 to 2.0 nanometers. Manufacture of free layer 535 continues atstep 442, where a W layer 537 is deposited. In an embodiment, W layer537 comprises a thin film of W having a thickness of 0.2 nanometers, andin other embodiments can have a thickness ranging from 0.1 to 1.0nanometers. At step 444, manufacture of free layer 536 continues withforming magnetic layer 539. In an embodiment, magnetic layer 539 cancomprise a thin film of CoFeB comprised of sixty percent iron (Fe),twenty percent cobalt (Co) and twenty percent boron (B), and having athickness of 0.9 nanometers. In other embodiments, magnetic layer 539can comprise a thin film of CoFeB or other suitable magnetic materialhaving a thickness ranging from 0.5 to 1.5 nanometers.

Collectively, magnetic layers 535 and 539, along with nonmagnetic Wlayer 537, form free magnetic layer 536. Free magnetic layer 536 has amagnetic vector having a magnetic direction perpendicular to its plane.In addition, free magnetic layer 536 design may include magnetization ofthe free layer 536 pointing a few degrees away from its perpendicularaxis. The tilted angle of the free layer magnetization can be due tointeraction with the PSC magnetic layer 550 or due to magnetocrystallineanisotropy, will additionally help switching of the free layermagnetization by improving the initiation of the switching. As seen inFIG. 7, the magnetic direction of free magnetic layer 536 can switch onehundred eighty (180) degrees from one direction to another,antiparallel, direction.

After fabrication of magnetic tunnel junction 530 at step 438, step 446is performed in which a nonmagnetic spacer layer 540 is deposited. In anembodiment, nonmagnetic spacer layer 540 can comprise a thin film of MgOhaving a thickness of 0.9 nanometers. In other embodiments, spacer layer540 can comprise a thin film of MgO having a thickness ranging from 0.5to 1.5 nanometers. In other embodiments, spacer layer 540 can beconstructed as described in U.S. patent application Ser. No. 14/866,359,filed Sep. 25, 2015, and entitled “Spin Transfer Torque Structure ForMRAM Devices Having A Spin Current Injection Capping Layer.” U.S. patentapplication Ser. No. 14/866,359 is hereby incorporated by reference inits entirety.

After deposition of spacer layer 540, precessional spin current magneticstructure 550 is deposited (step 450). As seen in FIG. 6B, manufactureof precessional spin current magnetic structure 550 comprises severalsteps. At step 452, first precessional spin current ferromagnetic layer543 is fabricated over spacer layer 540. In an embodiment, firstprecessional spin current ferromagnetic layer 543 comprises a thin filmof Fe having a thickness of 0.4 nanometers. In other embodiments, firstprecessional spin current ferromagnetic layer 543 can comprise a thinfilm of Fe having a thickness ranging from 0.5 to 2.0 nanometers.

At step 454, nonmagnetic precessional spin current insertion layer 545is deposited over magnetic Fe layer 543. In an embodiment, nonmagneticprecessional spin current insertion layer 545 can comprise a thin filmof Ru having a thickness of 1.5 nanometers. As will be discussed, thethickness of nonmagnetic precessional spin current insertion layer 545can be selected to control and tune the coupling of the firstprecessional spin current ferromagnetic layer 543 to the secondprecessional spin current ferromagnetic layer 547 (described below). Useof nonmagnetic precessional spin current insertion layer 545 providesseveral improvements and advantages. For example, nonmagneticprecessional spin current insertion layer 545 enables precessional spincurrent magnetic structure 550 to utilize a spin pumping mechanism tocontrol the spin torque efficiency of precessional spin current magneticstructure 550. Nonmagnetic precessional spin current insertion layer 545also enables decreasing of dipolar fringing fields from precessionalspin current magnetic structure 550 acting on free layer 536 due to thethickness of separation between the first precessional spin currentferromagnetic layer 543 and free layer 536. Strong fringing fields arean unwanted effect and can prevent free layer 536 from switching undernormal operating conditions because of the large dipolar magnetic fieldacting on free layer 536.

While the nonmagnetic precessional spin current insertion layer 545 ofthe embodiment shown in FIG. 7 can be constructed of Ru, othernonmagnetic materials having a relatively long spin diffusion length,e.g., greater than five nanometers, can also be used. Examples of suchnonmagnetic materials include Cu (which has a spin diffusion length ofapproximately 400 nm), Ag (which has a spin diffusion length ofapproximately 150 nm), Au (which has a spin diffusion length ofapproximately 35 nm), Mg (which has a spin diffusion length ofapproximately 150 nm) and Al (which has a spin diffusion length ofapproximately 300 nm). Ru, described above, has a spin diffusion lengthof approximately ten (10) nm. Use of materials like these, which have arelatively long spin diffusion length, makes it possible to achievedesired spin torque efficiency of precessional spin current magneticstructure 550 via dynamic coupling due to the spin pumping effect.

At step 456, second precessional spin current ferromagnetic layer 547 isdeposited. In an embodiment, second precessional spin currentferromagnetic layer 547 comprises a thin film of CoFeB comprised offorty percent iron (Fe), forty percent cobalt (Co) and twenty percentboron (B), and having a thickness of 1.7 nanometers. In otherembodiments, second precessional spin current ferromagnetic layer 547can comprise of a thin film of CoFeB, Co, Fe, Ni and their alloys havinga thickness ranging between 1.0 to 5.0 nanometers.

Note that spacer layer 540 is used for effective injection of spinpolarized current into magnetic tunnel junction 530 from precessionalspin current magnetic structure 550. Spin current is generated byprecessing the magnetization direction of second precessional spincurrent ferromagnetic layer 547 and carried by spin diffusive transportthrough nonmagnetic precessional spin current insertion layer 545 intofirst precessional spin current ferromagnetic layer 543 using spinpumping effect. The second precessional spin current ferromagnetic layer547 and first precessional spin current ferromagnetic layer 543magnetizations become dynamically coupled via spin pumping mechanism.First precessional spin current ferromagnetic layer 543 serves as a spincurrent injection layer, which provides continuity of the spin currentgenerated by second precessional spin current ferromagnetic layer 547.

Note also that when nonmagnetic precessional spin current insertionlayer 545 has a thickness above approximately one nanometer, theexchange coupling between first precessional spin current ferromagneticlayer 543 and second precessional spin current ferromagnetic layer 547is significantly reduced. However, when nonmagnetic precessional spincurrent insertion layer 545 has a thickness above approximately onenanometer, dynamic coupling between second precessional spin currentferromagnetic layer 547 and first precessional spin currentferromagnetic layer 543 via the spin pumping effect becomes dominant.Thus, using a precessional spin current magnetic structure 550 having afirst precessional spin current ferromagnetic layer 543 and secondprecessional spin current ferromagnetic layer 547 separated bynonmagnetic precessional spin current insertion layer 545 providesbetter control and allows for tuning of the coupling between theprecessional spin current magnetic structure 550 and free layer 536.

After manufacture of precessional spin current magnetic structure 550 atstep 450, a capping layer 551 is deposited (step 460). Manufacture ofcapping layer 551 can comprise depositing TaN layer 553 (step 462) anddepositing Ru layer 555 (step 464). In an embodiment, TaN layer 553comprises a thin film of TaN having a thickness of 2.0 nanometers, whilein other embodiments, TaN layer 553 can have a thickness ranging from1.0 to 5.0 nanometers. In an embodiment, Ru layer 555 comprises a thinfilm of Ru having a thickness of ten (10) nanometers, while in otherembodiments, Ru layer 555 can have a thickness ranging from 1.0 to 20nanometers. In other embodiments, capping layer 551 comprise a layer ofRu (with no TaN) or a layer of MgO. The selection of a particularcapping structure is influenced, among several reasons, by theparticular annealing temperature to be used. This is due to the factthat these particular materials will have different characteristicsdepending on the annealing temperature.

At step 466, a hard mask 557 is deposited. Hard mask 557 can compriseTaN. Thereafter, at step 468, MTJ stack 500 is annealed at 300 degreesCelsius for one hour. Such a device, after annealing, had a tunnelingmagnetoresistance (TMR) above 100% with resistance area product (RA)range of 5-10 Ωμm². Current can be provided by a current source 575.

A flowchart showing a method 600 of manufacturing an embodiment of anMRAM stack 700 is illustrated in FIGS. 8A-8B. MRAM stack 700 willnormally be fabricated on some form of substrate, which in certainembodiments can be a silicon substrate, and can include complementarymetal oxide semiconductor (CMOS) circuitry fabricated thereon. MRAMstack 700 is illustrated in FIG. 9. First step 602 is to deposit seedlayer 720. In an embodiment, seed layer 720 can be constructed bydepositing, at step 604, a TaN layer 704 and then, at step 606,depositing a Cu layer 706. In an embodiment, TaN layer 704 is a thinfilm having a thickness of ten nanometers and Cu layer 706 is a thinfilm having a thickness of three nanometers. In alternative embodiments,TaN layer 704 can have a thickness ranging from 2.0 to 20 nanometerswhile Cu layer 706 can have a thickness ranting from 0 to 20 nanometers.

At step 608, first perpendicular synthetic antiferromagnetic layer 722is deposited. In an embodiment, first perpendicular syntheticantiferromagnetic layer 722 can comprise a Pt layer 708 (deposited atstep 610), a Co/Pt multilayer 710 (deposited at step 612) and a Co layer712 (deposited at step 614). In an embodiment, Pt layer 708 is a Pt thinfilm having a thickness of 0.7 nanometers. In other embodiments, Ptlayer 708 can comprise a Pt thin film having a thickness ranging from0.5 to 20 nanometers. Co/Pt multilayer 710 can comprise a thin film ofCo having a thickness of 0.6 nanometers and a thin film of Pt having athickness of 0.4 nanometers. In other embodiments, the Co layer of Co/Ptmultilayer 710 can have a thickness of 0.1 to 1.0 nanometers and the Ptlayer of Co/Pt multilayer 710 can have a thickness ranging from 0.1 to1.0 nanometers. In an embodiment, Co/Pt multilayer 710 is repeated suchthat Co/Pt multilayer 710 comprises six Co/Pt multilayers. In anembodiment, Co layer 712 is a thin film having a thickness of 0.6nanometers. In other embodiments, Co layer 712 can have a thicknessranging from 0.1 to 1.0 nanometers.

As seen in FIG. 9, first perpendicular synthetic antiferromagnetic layer722 has a magnetic vector having a direction perpendicular to its plane.The magnetic direction of first perpendicular syntheticantiferromagnetic layer 722 is fixed and will not change directions(i.e., rotate or precess) under normal operating conditions. Thethickness of synthetic antiferromagnetic layers can be chosen such as tominimize the dipolar fringing fields emerging from the reference layerand other magnetic layers within MTJ structure which act on a free layerafter device fabrication

At step 616, exchange coupling layer 724 is deposited. In an embodiment,exchange coupling layer 724 comprises an Ru thin film having a thicknessof 0.8 nanometers, and in other embodiments can range from 0.3 to 1.5nanometers.

At step 618, second perpendicular synthetic antiferromagnetic layer 726is fabricated. Fabrication of second perpendicular syntheticantiferromagnetic layer 726 (step 618) comprises many steps, andincludes fabrication of reference layer 732 of magnetic tunnel junction730, as will be discussed. At step 620, Co layer 514 is deposited. In anembodiment, Co layer 714 is a thin film having a thickness of 0.3nanometers and in other embodiments, can have a thickness of 0.1 to 1.0nanometers. Thereafter, at step 620, a Co/Pt multilayer 716 isdeposited. In an embodiment, Co/Pt multilayer 716 comprises a thin filmof Co having a thickness of 0.6 nanometers and a thin film of Pt havinga thickness of 0.4 nanometers. In other embodiments, the thin film of Cocan have a thickness of 0.1 to 1.0 nanometers while the thin film of Ptcan have a thickness of 0.1 to 1.0 nanometers. Moreover, Co/Ptmultilayer 716 can comprise multiple Co/Pt layers as described herein.In an embodiment, Co/Pt multilayer 716 has two Co/Pt multilayers withthe thickness properties described above. After depositing Co/Ptmultilayer 716 at step 622, the method described herein deposits acobalt layer 718 at step 624. In an embodiment, Co layer 718 is a thinfilm having a thickness of 0.9 nanometers, while other embodiments, Colayer 718 can have a thickness in the range of 0.1 to 1.0 nanometers.

Together, Co layer 714, Co/Pt layer 716 and Co layer 718 form a magneticstructure. The magnetic direction of the combination of Co layer 714,Co/Pt layer 716 and Co layer 718 is fixed, perpendicular to the plane ofeach layer (although variations of a several degrees are within thescope of what is considered perpendicular), and antiparallel to themagnetic direction of first perpendicular synthetic antiferromagneticlayer 722. The magnetic properties of the combination of Co layer 714,Co/Pt layer 716 and Co layer 718 will interact with the magneticproperties of reference layer 732 of second perpendicular syntheticantiferromagnetic layer 726 to generate a magnetic vector having a fixedmagnetic direction that is also perpendicular to the plane of each layerof second perpendicular synthetic antiferromagnetic layer 726 andantiparallel to the magnetic direction of first perpendicular syntheticantiferromagnetic layer 722. These magnetic vectors are illustrated andFIG. 9, where it can be seen that the second perpendicular syntheticantiferromagnetic layer 726 has a fixed and perpendicular magneticdirection that is antiparallel to the magnetic direction of firstperpendicular synthetic antiferromagnetic layer 722. Note that themagnetic directions of second perpendicular synthetic antiferromagneticlayer 726 and first perpendicular synthetic antiferromagnetic layer 722are fixed under normal operating conditions.

After deposition of Co layer 718 at step 624, reference layer 732 isdeposited (step 628). Step 628, fabrication of reference layer 732,comprises several steps, including deposition of a tungsten (W) layer729 (step 632) and deposition of magnetic layer 731 (step 634). In anembodiment, W layer 729 comprises a thin film having a thickness of 0.3nanometers. In an embodiment, magnetic layer 731 comprises a thin filmof CoFeB comprised of sixty percent iron (Fe), twenty percent cobalt(Co) and twenty percent boron (B), where the thin film has a thicknessof 0.8 nanometers. In other embodiments, W layer 729 can comprise a thinfilm having a thickness of 0.2 to 1.0 nanometers, and magnetic layer 731can comprise a thin film of CoFeB having a thickness of 0.5 to 1.5nanometers.

Reference layer 732 is constructed using magnetic materials so that ithas a magnetic vector having a magnetic direction perpendicular to itsplane, is fixed in direction, and is antiparallel to the magneticdirection of first perpendicular synthetic antiferromagnetic layer 722.As discussed and as seen in FIG. 9, the collective materials of thesecond perpendicular synthetic antiferromagnetic layer 726 have amagnetic vector having a magnetic direction that is perpendicular to theplane of each of its collective layers, is fixed in direction andantiparallel to the magnetic direction of first perpendicular syntheticantiferromagnetic layer 722. Note that the particular magnetic directionof first perpendicular synthetic antiferromagnetic layer 722 and secondperpendicular synthetic antiferromagnetic layer 726 is not important, solong as they are perpendicular to their respective planes andantiparallel to each other.

As discussed, reference layer 732 is one of the structures formingmagnetic tunnel junction 730. The flowchart showing the method ofmanufacturing MRAM stack 700, including magnetic tunnel junction 730,continues on FIG. 8B. At step 636, nonmagnetic tunneling barrier layer734 is deposited on reference layer 732. In an embodiment, nonmagnetictunneling barrier 734 is formed as a thin film of an insulatingmaterial, e.g., MgO, and has a thickness of 1.1 nm. The purpose ofnonmagnetic tunneling barrier 734 is discussed above.

Manufacture of magnetic tunnel junction 730 continues at step 638, whenfree layer 736 is deposited over nonmagnetic tunneling barrier 734.Fabrication of free layer 736 comprises several steps. At step 640, amagnetic layer 735 is deposited over nonmagnetic tunneling barrier 734.In an embodiment, magnetic layer 735 is comprised of a thin film ofCoFeB comprised of fifty-four (54) percent iron (Fe), eighteen (18)percent cobalt (Co) and twenty-eight (28) percent boron (B), with thethin film having a thickness of 1.5 nanometers. In other embodiments,magnetic layer 735 can comprise a thin film of CoFeB or other suitablemagnetic material having a thickness ranging from 0.5 to 2.5 nanometers.Manufacture of free layer 735 continues at step 642, where a W layer 737is deposited. In an embodiment, W layer 737 comprises a thin film of Whaving a thickness of 0.5 nanometers, and in other embodiments can havea thickness ranging from 0.2 to 1.0 nanometers. At step 644, manufactureof free layer 736 continues with forming magnetic layer 739. In anembodiment, magnetic layer 739 can comprise a thin film of CoFeBcomprised of fifty-four (54) percent iron (Fe), eighteen (18) percentcobalt (Co) and twenty-eight (28) percent boron (B), with the thin filmhaving a thickness of 0.8 nanometers. In other embodiments, magneticlayer 739 can comprise a thin film of CoFeB or other suitable magneticmaterial having a thickness ranging from 0.5 to 2.0 nanometers.

Collectively, magnetic layers 735 and 739, along with nonmagnetic Wlayer 737, form free magnetic layer 736. Free magnetic layer 736 has amagnetic vector having a magnetic direction perpendicular to its plane.In addition, free magnetic layer 736 design may include magnetization ofthe free layer 736 pointing a few degrees away from its perpendicularaxis. The tilted angle of the free layer magnetization can be due tointeraction with the PSC magnetic layer 750 or due to magnetocrystallineanisotropy, will additionally help switching of the free layermagnetization by improving the initiation of the switching. As seen inFIG. 9, the magnetic direction of free magnetic layer 736 can switch onehundred eighty (180) degrees from one direction to another,antiparallel, direction.

After fabrication of magnetic tunnel junction 733 at step 638, step 646is performed in which a nonmagnetic spacer layer 740 is deposited. In anembodiment, nonmagnetic spacer layer 740 can comprise a thin film of MgOhaving a thickness of 0.9 nanometers. In other embodiments, spacer layer740 can comprise a thin film of MgO having a thickness ranging from 0.5to 2.0 nanometers. In other embodiments, spacer layer 740 can beconstructed as described in U.S. patent application Ser. No. 14/866,359,filed Sep. 25, 2015, and entitled “Spin Transfer Torque Structure ForMRAM Devices Having A Spin Current Injection Capping Layer.” U.S. patentapplication Ser. No. 14/866,359 is hereby incorporated by reference inits entirety.

After deposition of spacer layer 740, precessional spin current magneticstructure 750 is deposited (step 650). As seen in FIG. 8B, manufactureof precessional spin current magnetic structure 750 comprises severalsteps. At step 652, first precessional spin current ferromagnetic layer743 is fabricated over spacer layer 740. In an embodiment, firstprecessional spin current ferromagnetic layer 743 comprises a thin filmof Fe having a thickness of 0.6 nanometers. In other embodiments, firstprecessional spin current ferromagnetic layer 743 can comprise a thinfilm of Fe having a thickness ranging from 0.5 to 2.0 nanometers.

At step 654, nonmagnetic precessional spin current insertion layer 745is deposited over magnetic first precessional spin current ferromagneticlayer 743. In an embodiment, nonmagnetic precessional spin currentinsertion layer 745 can comprise a thin film of Ru having a thickness of1.5 nanometers. As discussed in the context of the embodiment shown inFIG. 7, nonmagnetic precessional spin current insertion layer 745provides several improvements and advantages. As discussed, nonmagneticprecessional spin current insertion layer 745 enables precessional spincurrent magnetic structure 750 to utilize a spin pumping mechanism tocontrol the spin torque efficiency of precessional spin current magneticstructure 750. As also discussed, nonmagnetic precessional spin currentinsertion layer 745 also enables the spin pumping mechanism to coupleprecession of second precessional spin current ferromagnetic layer 747(discussed below) to first precessional spin current ferromagnetic layer743, thus allowing for the spin torque to be injected from theprecessional spin current magnetic structure 750 into free layer 736using nonmagnetic spacer layer 740.

While the nonmagnetic precessional spin current insertion layer 745 ofthe embodiment shown in FIG. 9 is constructed of Ru, other nonmagneticmaterials having a relatively long spin diffusion length, e.g., greaterthan five nanometers, can also be used. Examples of such nonmagneticmaterials include Cu (which has a spin diffusion length of approximately400 nm), Ag (which has a spin diffusion length of approximately 150 nm),Au (which has a spin diffusion length of approximately 35 nm), Mg (whichhas a spin diffusion length of approximately 150 nm) and Al (which has aspin diffusion length of approximately 300 nm). Ru, described above, hasa spin diffusion length of approximately ten (10) nm. Use of materialslike these, which have a relatively long spin diffusion length, makes itpossible to achieve the desired spin torque efficiency of precessionalspin current magnetic structure 750 via dynamic coupling due to the spinpumping effect.

At step 656, second precessional spin current ferromagnetic layer 747 isdeposited. In an embodiment, second precessional spin currentferromagnetic layer 747 comprises a thin film of CoFeB comprised offorty percent iron (Fe), forty percent cobalt (Co) and twenty percentboron (B), and having a thickness of 1.85 nanometers. In otherembodiments, second precessional spin current ferromagnetic layer 747can comprise of a thin film of CoFeB, Co, Fe, Ni and their alloys havinga thickness ranging between 1.0 to 5.0 nanometers.

Just as in the device 500 shown in FIG. 7, spacer layer 740 is used foreffective injection of spin polarized current into magnetic tunneljunction 730 from precessional spin current magnetic structure 750. Asdiscussed, spin current is generated by precessing the magnetizationdirection of second precessional spin current ferromagnetic layer 747and carried by spin diffusive transport through nonmagnetic precessionalspin current insertion layer 745 into first precessional spin currentferromagnetic layer 743 using spin pumping effect. The secondprecessional spin current ferromagnetic layer 747 and first precessionalspin current ferromagnetic layer 743 magnetizations become dynamicallycoupled via a spin pumping mechanism. First precessional spin currentferromagnetic layer 743 serves as a spin current injection layer, whichprovides continuity of the spin current generated by second precessionalspin current ferromagnetic layer 747. As also discussed above regardingthe device embodiment 500 of FIG. 7, the thickness of the nonmagneticprecessional spin current insertion layer 745 can be selected to selectthe desired amount of coupling of the second precessional spin currentferromagnetic layer 747 to the first precessional spin currentferromagnetic layer 743, which in turn can be used to tune the couplingof precessional spin current magnetic structure 750 to free layer 736.

After manufacture of precessional spin current magnetic structure 750 atstep 650, a capping layer 751 is deposited (step 660). Manufacture ofcapping layer 751 can comprise depositing TaN layer 753 (step 662) anddepositing Ru layer 755 (step 664). In an embodiment, TaN layer 753comprises a thin film of TaN having a thickness of 2.0 nanometers, whilein other embodiments, TaN layer 753 can have a thickness ranging from1.0 to 5.0 nanometers. In an embodiment, Ru layer 755 comprises a thinfilm of Ru having a thickness of ten (10) nanometers, while in otherembodiments, Ru layer 755 can have a thickness ranging from 1.0 to 20nanometers. In other embodiments, capping layer 751 comprise a layer ofRu (with no TaN) or a layer of MgO. As discussed, the selection of aparticular capping structure is influenced, among several reasons, bythe particular annealing temperature to be used. This is due to the factthat these particular materials will have different characteristicsdepending on the annealing temperature.

At step 666, MTJ stack 700 is annealed at 400 degrees Celsius for up toforty-five (45) minute soak time using in-situ rapid thermal annealingoven. At step 668, hard mask 757 is deposited. Hard mask 757 cancomprise a layer of TaN having a thickness of 7.0 nanometers. Theacceptable range of temperatures for the annealing step is within therange of 250 degrees Celsius to 450 degrees Celsius. Current can beprovided by a current source 775.

The MTJ stack 700 manufactured as described with the high temperatureannealing step 666 results in a device 700 having tunnelingmagnetoresistance (TMR) of above one hundred sixty (160) percent (whichis advantageously high) and a resistance area product (RA) range up toapproximately ten (10) to twelve (12) Ωμm². These TMR and RAcharacteristics of device 700 are highly desirable and indicate thatprecessional spin current magnetic structure 750 as described herein canwithstand high temperature annealing at 400 degrees Celsius and stillperform well. This means that a MTJ device 700 with precessional spincurrent magnetic structure 750 can fabricated using a standard CMOSprocess. This is very advantageous since it means that custommanufacturing facilities are not required, and also means that MRAMmemory can be embedded in CMOS integrated circuits.

FIG. 11 is a graph of the thin film vibrating sample magnetometer (VSM)major hysteresis loop data for magnetic device 500 having magnetictunnel junction 530 and precessional spin current magnetic structure550. To obtain this VSM major hysteresis loop (labeled as 1100 in FIG.11), a magnetic field was applied with a magnetic direction that wasperpendicular to the sample plane i.e. along easy axis of magnetictunnel junction 530. As seen in FIG. 11, the applied magnetic fieldstarted at −12,000 Oersteds, which then decreased to 0.00 Oersteds,before rising to +12,000 Oersteds, another very large magnetic field.The magnetic field was then decreased from +12,000 Oersteds to 0.00Oersteds, and then increased to −12,000 Oersteds. Positive and negativesigns of the DC applied field indicate perpendicular applied fielddirections of the field sweep.

Switching of the magnetic direction of particular components of the pMTJis shown schematically by the arrows. Any switching of the magneticdirection of first perpendicular synthetic antiferromagnetic layer 522is shown with the arrows 1110A, 1110B and 1110C, each of whichillustrates the magnetic direction of the layer. Any switching of themagnetic direction of second perpendicular synthetic antiferromagneticlayer 526 is shown with the arrows 1120A, 1120B and 1120C, each of whichillustrates the magnetic direction of the layer. Finally, any switchingof free layer 536 is shown with the arrows 1130A, 1130B and 1130C, eachof which illustrates the magnetic direction of the layer.

As is seen in FIG. 11, as the perpendicular magnetic field is decreasedfrom −12,000 Oersteds, the magnetic direction first perpendicularsynthetic antiferromagnetic layer 522, does not reverse directions untilthe magnetic field measures approximately +4,000 Oersteds. This is shownby arrow 1110C, illustrating that the magnetic direction of firstperpendicular synthetic antiferromagnetic layer 522 has switched. Thisdemonstrates first perpendicular synthetic antiferromagnetic layer 522is very stable since it would not experience such conditions undernormal use. This stability demonstrates that use of precessional spincurrent magnetic structure 550 does not negatively impact the stabilityof the entire reference layer 532 and its exchange coupling field.

As also seen in FIG. 11, second perpendicular syntheticantiferromagnetic layer 526 does not reverse directions until aperpendicular magnetic field of approximately −4,000 Oersteds isapplied. This is shown by arrow 1120A, illustrating that the magneticdirection of second perpendicular synthetic antiferromagnetic layer 526has switched. Because a device 500 will not experience such a largemagnetic field under normal operating conditions, this test demonstratesthat the second perpendicular synthetic antiferromagnetic layer 526 isvery stable, which also demonstrates that use of precessional spincurrent magnetic structure 550 does not negatively impact other magneticstructures in device 500. This is also important since the referencelayer 532 contained in second perpendicular synthetic antiferromagneticlayer 526 must have a fixed magnetic direction for the magnetic tunneljunction 530 to function properly.

Finally, FIG. 11 demonstrates that device 500, including precessionalspin current magnetic structure 550, has excellent free layer switchingperformance. Switching of free layer occurs at approximately 0.00Oersteds, and is illustrated by arrow 1130B.

Sharp switching transitions indicate good perpendicular anisotropies offirst perpendicular synthetic antiferromagnetic layer 522, referencelayer 532 (including second perpendicular synthetic antiferromagneticlayer 526) and free layer 536 of the perpendicular magnetic tunneljunction 530. Exchange coupling of 4.3 kOe indicates good stability ofthe reference layer. A slope of the hysteresis loop between ±3.0 kOeindicates a rotation of precessional spin current magnetic structure 550which is orthogonal to the layers of perpendicular magnetic tunneljunction 530, i.e., along hard axis of the perpendicular applied field.

FIG. 12 is a graph of the thin film vibrating sample magnetometer (VSM)major hysteresis loop data for magnetic device 500 having magnetictunnel junction 530 and precessional spin current magnetic structure550. To measure the VSM major hysteresis loop (labeled as 1200 in FIG.12), a magnetic field was applied with a magnetic direction that was inthe plane of the layers of magnetic tunnel junction 530. As seen in FIG.12, the applied magnetic field started at −14,000 Oersteds, which thendecreased to 0.00 Oersteds, before rising to +14,000 Oersteds, anothervery large magnetic field. The applied field was then decreased steadilyfrom +12,000 Oersteds to 0.00 Oersteds, before increasing to −12000Oersteds. The magnetic field was then decreased from +14,000 Oersteds to0.00 Oersteds, and then increased to −14,000 Oersteds. Positive andnegative signs of the DC applied field indicate in-plane applied fielddirections of the field sweep.

Increasing slope of the VSM major hysteresis loop 1200 corresponds tothe slow rotation of the layers of magnetic tunnel junction 530 when themagnetic field is applied in-plane, which is orthogonal to the magneticdirection of those layers. The sharp transition of the VSM majorhysteresis loop 1200 around zero field corresponds to precession of theprecessional spin current magnetic structure 550. This sharp switchingindicates that precessional spin current magnetic structure 550 isin-plane magnetized, i.e., along the easy axis of the in-plane appliedmagnetic field. In addition to the description above, the VSM majorhysteresis loops 1100 and 1200 shown in FIGS. 11 and 12 demonstrate thatfree layer 530 and precessional spin current magnetic structure 550 areorthogonally magnetized with respect to each other.

FIG. 13 shows the ferromagnetic resonance of a magnetic tunnel junctiondevice 500 having precessional spin current magnetic structure 550measured at twenty four (24) GHz. The magnetic field was applied inperpendicular direction. Dashed line 1300 at 8000 Oersteds indicates theregion boundary ω/γ˜8.0 kGauss at 24 GHz between in-plane precessionalspin current magnetic structure 550 and perpendicular magnetized freemagnetic layer 536. Because free layer 536 has a magnetic directionperpendicular to its plane, the resonance line occurs in the resonancefield below the ω/γ˜8.0 kGauss boundary according to the resonanceequation: ω/γ=H_(res)−4πM_(eff). Similarly precessional spin currentmagnetic structure 550 resonance will occur in the field above theω/γ˜8.0 kGauss boundary indicating strong in-plane magnetization. Theeffective magnetization values indicate strong perpendicular anisotropyof the free layer 536 (4πM_(eff)˜−3.5 kGauss) and strong in-planeanisotropy of precessional spin current magnetic structure 550(4πM_(eff)˜6 kGauss).

An alternative embodiment is shown in FIG. 14. In this embodiment,magnetic device 1400 has had its MTJ stack inverted with respect to theembodiment shown in FIG. 5. In particular, magnetic device 1400 includesa seed layer 1470. Precessional spin current magnetic structure 1450 isplaced over seed layer 1470. PSC structure 1450 comprises a firstprecessional spin current ferromagnetic layer 1447, a nonmagnetic PSCinsertion layer 1445 and a second precessional spin currentferromagnetic layer 1443. First precessional spin current ferromagneticlayer 1447 is similar to the second precessional spin currentferromagnetic layers 347, 547 and 747 described in the context of FIGS.5, 7 and 9, respectively. Nonmagnetic PSC insertion layer 1445 issimilar to the nonmagnetic PSC insertion layers 345, 545 and 747described in the context of FIGS. 5, 7 and 9. Finally, secondprecessional spin current ferromagnetic layer 1443 is similar to firstprecessional spin current ferromagnetic layer 343, 543 and 743 describedin the context of FIGS. 5, 7 and 9, respectively. Precessional spincurrent magnetic structure 1450 operates as described in the context ofcorresponding precessional spin current magnetic layers 350, 550 and750.

Nonmagnetic spacer layer 1440 is placed over PSC structure 1450.Nonmagnetic spacer layer 1440 has the same properties, construction andcharacteristics as nonmagnetic spacer layer 340, 540 and 740, discussedabove. MTJ 1430 is placed over nonmagnetic spacer layer 1440. MTJ 1430is generally constructed of free layer 1436 (which is placed overnonmagnetic spacer layer 1440) and reference layer 1432. Free layer 1436and reference layer 1432 are spatially separated from each other bytunneling barrier layer 1434, which is made of an insulating materialsuch as MgO or W. As above, MTJ 1430 as a perpendicular MTJ in that themagnetic direction of both reference layer and free layer areperpendicular to their respective planes. As discussed with respect toother embodiments, free magnetic layer 1436 design may includemagnetization of the free layer 1436 pointing a few degrees away fromits perpendicular axis. The tilted angle of the free layer magnetizationcan be due to interaction with the PSC magnetic layer 1450 or due tomagnetocrystalline anisotropy, will additionally help switching of thefree layer magnetization by improving the initiation of the switching.Ferromagnetic coupling layer 1428 is placed over reference layer 1432. Asynthetic antiferromagnetic (SAF) layer 1426 is disposed overferromagnetic coupling layer 1428. An antiferromagnetic coupling layer1424 is placed over SAF layer 1426. Another synthetic antiferromagneticlayer 1422 is placed over antiferromagnetic coupling layer 1424. Notethat SAF layer 1426 technically also includes ferromagnetic couplinglayer 1428 and reference layer 1432, but are shown separately here forexplanation purposes. SAF layers 1426 and 1422 also have perpendicularmagnetic directions under normal operating conditions. Finally, cappinglayer 1420 is placed over SAF layer 1422. Current can be provided by acurrent source 1475. Other than the ordering of the layers, magneticdevice operates in the same manner as described with respect to theembodiment shown in FIGS. 5, 7 and 9. Thus, just as shown in FIGS. 5, 7and 9, PSC magnetic structure 1450 rotates in such a way that spintransfer torque 310 is applied in a beneficial manner throughout theentire precession cycle of free layer 1436.

All of the layers of devices 300, 500, 700 and 1400 illustrated in FIGS.5, 7, 9 and 14 can be formed by a thin film magnetron sputter depositionsystem as would be appreciated by one skilled in the art. The thin filmsputter deposition system can include the necessary physical vapordeposition (PVD) chambers, each having one or more targets, an oxidationchamber and a sputter etching chamber. Typically, the sputter depositionprocess involves a sputter gas (e.g., argon, krypton, xenon or the like)with an ultra-high vacuum and the targets can be made of the metal ormetal alloys to be deposited on the substrate. Thus, when the presentspecification states that a layer is placed over another layer, suchlayer could have been deposited using such a system. Other methods canbe used as well. It should be appreciated that the remaining stepsnecessary to manufacture MTJ stacks 300, 500, 700 and 1300 arewell-known to those skilled in the art and will not be described indetail herein so as not to unnecessarily obscure aspects of thedisclosure herein.

It should be appreciated to one skilled in the art that a plurality ofMTJ structures 300, 500, 700 and 1300 can be manufactured and providedas respective bit cells of an STT-MRAM device. In other words, each MTJstack 300, 500, 700 and 1400 can be implemented as a bit cell for amemory array having a plurality of bit cells.

The above description and drawings are only to be consideredillustrative of specific embodiments, which achieve the features andadvantages described herein. Modifications and substitutions to specificprocess conditions can be made. Accordingly, the embodiments in thispatent document are not considered as being limited by the foregoingdescription and drawings.

What is claimed is:
 1. A magnetic device, comprising a first syntheticantiferromagnetic structure in a first plane, the first syntheticantiferromagnetic structure including a magnetic reference layer, themagnetic reference layer having a magnetization vector that isperpendicular to the first plane and having a fixed magnetizationdirection; a nonmagnetic tunnel barrier layer in a second plane anddisposed over the magnetic reference layer; a free magnetic layer in athird plane and disposed over the nonmagnetic tunnel barrier layer, thefree magnetic layer having a magnetization vector that is perpendicularto the third plane and having a magnetization direction that can precessfrom a first magnetization direction to a second magnetizationdirection, the magnetic reference layer, the nonmagnetic tunnel barrierlayer and the free magnetic layer forming a magnetic tunnel junction; anonmagnetic spacer layer in a fourth plane and disposed over the freemagnetic layer, the non-magnetic spacer layer comprising MgO; aprecessional spin current magnetic structure in a fifth plane that isphysically separated from the free magnetic layer, and magnetically andelectronically coupled to the free magnetic layer by the nonmagneticspacer layer, the precessional spin current magnetic structure having amagnetization vector with a magnetization direction in the fifth planewhich can freely rotate in any magnetic direction in the fifth plane,the precessional spin current magnetic structure comprising a firstprecessional spin current ferromagnetic layer, a nonmagneticprecessional spin current insertion layer and a second precessional spincurrent ferromagnetic layer, the first precessional spin currentferromagnetic layer being disposed over the nonmagnetic spacer layer,the nonmagnetic precessional spin current insertion layer being disposedover the first precessional spin current ferromagnetic layer, and thesecond precessional spin current ferromagnetic layer being disposed overthe nonmagnetic precessional spin current insertion layer, wherein thenonmagnetic precessional spin current insertion layer is constructed ofa thin film of Ru; and a capping layer in a sixth plane and disposedover the precessional spin current magnetic structure; wherein electronsof an electrical current passing through the precessional spin currentmagnetic structure are aligned in the magnetic direction of theprecessional spin current magnetic and injected into the nonmagneticspacer, the free magnetic layer, the nonmagnetic tunnel barrier layer,and the magnetic reference layer, and wherein the magnetizationdirection of the precessional spin current magnetic structure precessesand is free to follow precession of the magnetization direction of thefree magnetic layer, thereby causing spin transfer torque to assistswitching of the magnetization vector of the free magnetic layer.
 2. Themagnetic device of claim 1 wherein the nonmagnetic precessional spincurrent insertion layer is constructed of a material having a spindiffusion length exceeding two (2) nanometers.
 3. The magnetic device ofclaim 1 wherein the thin film of Ru has a thickness of at least onenanometer.
 4. The magnetic device of claim 1 wherein the thin film of Ruhas a thickness of 1.5 nanometers.
 5. The magnetic device of claim 1,wherein the first precessional spin current ferromagnetic layercomprises a thin film of Fe, the nonmagnetic precessional spin currentinsertion layer comprises a material with a long spin diffusion length,and the second precessional spin current ferromagnetic layer comprises athin film of CoFeB.
 6. The magnetic device of claim 5, wherein the thinfilm of Fe has a thickness of 0.4 nanometers.
 7. The magnetic device ofclaim 5, wherein the thin film of Fe has a thickness of 0.6 nanometers.8. The magnetic device of claim 5 wherein the thin film of CoFeB iscomprised of forty percent Co, forty percent Fe and twenty percent B. 9.The magnetic device of claim 8 wherein the thin film of CoFeB has athickness of 1.7 nanometers.
 10. The magnetic device of claim 8 whereinthe thin film of CoFeB has a thickness of 1.85 nanometers.
 11. Themagnetic device of claim 5, wherein the material with a long spindiffusion length is selected from the group consisting of Ru, Cu, Ag,Au, Mg and Al.
 12. The magnetic device of claim 1 wherein the freemagnetic layer has an effective magnetic anisotropy such that its easyaxis magnetization axis points away from the perpendicular direction andforms an angle with respect to perpendicular plane.